Thanks, RickE and Vee. I'll probably get a set of gaskets and install them at a later date.

Quick review of Time-Serts: I'm glad I got these instead of helicoils, at Vee's suggestion. They cost much more than helicoils and probably take twice as long to install. I repaired threads in two holes in about 90 minutes, but that included doing everything by hand with a tap wrench, like drilling out the old threads and cutting the counter-sunk holes. Next time, I'll do the counter-sunk holes with a drill. That's the part that took the longest. I'm confident that the new threads are stronger than the original ones were when they left the factory.

 

Mini update:
I ended up repairing all but one of the holes for the bolts holding the coils down with Time-Serts. Replaced the cam cover gasket and six spark plug boss seals with Jaguar OEM seals. Replaced all 13 bolt seals with new URO seals. Replaced all of the spark plugs with Champion RC12YCs, same as they were before. Replaced all of the coils with QYL coils. Installed coil gaskets.

I've only had one chance to actually drive the car since doing all that, but it drove perfectly smoothly for about 30 miles. Engine sounded good, no stalling, no sputtering, and it idled at 600 RPM.

The only issue I had was that the steering got very heavy away from center, say past 11 o'clock or 1 o'clock. I checked the power steering reservoir and filled it to the fill line with Mercon V ATF. Didn't see any leakage, but I'll keep an eye on that. Next time I have a chance to drive, I'll try to bleed the system and check for puddles.